It is well known in the art that wells in sandy, oil-bearing formations are frequently difficult to operate because the sand in the formation is poorly consolidated and tends to flow into the well with the oil. This "sand production" is a serious problem because the sand causes erosion and premature wearing out of the pumping equipment, and is a nuisance to remove from the oil at a later point in the production operation.
Furan resin has been used in situ chemical sand consolidation since the 1960's, as described in U.S. Pat. Nos. 3,199,590 and 3,209,826. Due to the reactivity of furan resin and it's incompatibility with water, early sand consolidation processes use a multi-slug injection, externally catalyzed procedure to ensure a strong resin sand adhesion and gelation rate control. An injection sequence of diesel oil preflush followed by resin injection, diesel oil spacer and catalyst is complicated and gives inconsistent results. In addition, this oil based process presented disposal and fire hazard problems. In the 1970's, the process was modified and the diesel oil was replaced by brine in the preflush and spacer injections. However, the success rate and reliability were not improved.
Commercial furan resin is in the prepolymer stage of furfuryl alcohol (FA), as described by Grayson, ed. "Kirk-Othmer Encyclopedia of Chemical Technology," 3rd edition, Vol. 11, pp. 499-527. Furan resin available from Quaker Oat Chemicals is polymerized to a viscosity of 240-270 centipoise (at 55.degree. C.). ##STR1##
The resinification of furan resin catalyzed by strong acids to form a thermally and chemically stable material is applied in the preparation of foundry cores and in the laminating of graphite and glass fibers. The polymerization reaction is highly exothermic and is difficult to control at high temperature. Typical foundry formulations with an internal phthaloyl chloride catalyst gel and set within 20 minutes at 25.degree. C. Up to about 18% water is produced in the polymerization of FA. The volume shrinkage and the moisture trapped in the laminating intersurfaces are some of the difficulties in furan resin applications.
U.S. Pat. No. 4,903,770 describes a furan based process for the sand consolidation in steam injected wells. It places a furfuryl alcohol/ester diluent/H.sub.2 SO.sub.4 mixture delivered with high quality steam after an ester-acid preflush to achieve a rapid consolidation near the perforations.
To use furan resin, the resin must be deposited uniformly on the surfaces of sand grains. The water in the formation and the water that is a reaction product must be removed effectively for a strong bonding between resin and sand. Formation water removal by displacement with diesel/surfactant is inefficient and costly. Resin placement by displacement with another fluid, such as diesel or brine, is not reliable in heterogeneous formations.
Therefore, it is an object of the present invention to provide a reliable resin placement method. It is a further object of the present invention to provide a sand consolidation method which is less wasteful.